Interaction of optical signals with metallic nanostructures and metal surfaces plays an important role in the emerging fields of plasmonics, metal optics, and optical metamaterials. Collective oscillation of conduction electrons in metal due to their interaction with optical signals leads to various exciting features, such as optical field confinement and enhancement, due to the local and surface Plasmon resonances. Plasmonic nanostructures are also the integral parts of building blocks in optical metamaterials with unconventional effective parameter values, such as negative or near zero permittivity, permeability and/or refractive index. The permittivity of most of the noble metals is believed to have a negative real part, which suggests the possibility of new materials having interesting properties associated with it. However nobel metals also exhibit significant ohmic losses, which are represented by the imaginary parts of their permittivity functions. These ohmic losses in part prevent noble metallic nanostructures being used for manipulating optical signals.
Independent of the field of optical signals and metallic nanostructures, some groups have been studying graphene, which is a single atomically thin layer of carbon. Graphene has recently been shown to exhibit interesting conductive properties, one of which is a complex conductivity, σg=σg,r+iσg,i, which depends on radian frequency ω, charged particle scattering rate Γ representing loss mechanism, temperature T, and chemical potential μc which depends on the carrier density controllable by a gate voltage and/or chemical doping. An interesting feature of the conductivity of graphene is that its imaginary part, i.e., σg,i, can attain both negative and positive values in different ranges of frequency for different gate voltages, different chemical potentials and temperatures.